Electric arc furnace



Aug. 29, 1939.

K. SCHNEIDER El" AL 2,171,435

ELECTRIC ARC FURNACE Filed Jan. 23, 1937 PD g Kari Schneider HermannSchunck lnvemons By TlzeirA fforbeys a g k Patented Aug. 29, 1939 UNITEDSTATES PATENT OFFICE ELECTRIC ARC FURNACE Kurt Schneider and HermannSchunck, Bitterfeld, Germany, assignors to I. G. Farbenindnstrie Main,Germany Aktiengesellschaft,

Frankfort-on-the- 1 Claim.

This invention relates to a method of and means for magnetically blowingelectric arcs on metal electrodes.

When metal electrodes are employed in elec" 5 tric arc furnaces, it isnecessary to cause the points where the arc is struck to migrate overthe electrodes, in order to prevent them from fusing under the influenceof the temperatures generated at the striking point. This migration 1can be effected by blowing the are, by means of a current of gas bymechanically moving, for example rotating, the electrodes or bygenerating in the proximity of the are, a magnetic field energised bydirect or alternating current. In

the last-named method however, the generating of said field by meanssuch as electromagnets' separated and remote from the electrodesthemselves, entails, especially in the case of electric furnaces of thecovered type, a corresponding modification in the furnace design, inorder to accommodate the electromagnets. This imposes limitations on theform of the furnace chamber which are frequently inconvenient orundesir-- able. 0n the other hand when the energising coil is situatedoutside the shell of the furnace difllculties are encountered inadequately heatinsulating the shell.

The present invention aims at obviating the necessity of providingarc-blowing means separate from the electrodes and the disadvantagesconsequent thereon, by generating the electromagnetic blowing field inthe electrode itself by means of an electric current circulating roundor passing through the electrode.

This arrangement, in which the means energlsing themagnetic field froman integral unit with the electrode, does not in any way interfere withthe normal furnace design. For example, in the case of shaft furnaces,the shell may be provided with heat-insulating layers of any convenientthickness, or in the case of drum furnaces, which are particularlyfavoured in view of their thermal economy, such furnaces may beequipped" with metalelectrodes, which 'was hitherto consideredimpossible. Gas-reaction furnaces too, can be of particularly simpledesign, since-the reaction chamber can be designed solely with a view toobtaining optimum con- 5 ditions of flow in the gas space, withouthaving to take into consideration the restrictions otherwise imposed bythe accommodation of the electromagnetic blowing mean's.

In order more clearly to understand the in- 55 vention, reference ismade to the accompanying drawing which illustrates diagrammatically andby way of example an embodiment thereof.

The metal electrodes E1 and E: are of the known hairpin design.

B and C denote respectively the inand out- I leads for the workingcurrent generating the are L between the hairpin electrodes E1 and E2,the path of said current being therefore from B to C via L. An auxiliaryenergising current, of high strength and very low oltage indicated by 10U in the drawing, is generated in the annular conductorD, E, F, by anysuitable source Q of high intensity, low voltage direct oralternatingcurrent, which source is preferably located at the point of entry of theelectrode into the furnace chamber (1. e. between D and F). This sourcemay, in the case of direct current, be a thermo-element. This auxiliarycurrent generates the magnetic field, represented by annular arrows Ksurrounding the electrode E1. 20

This construction results in the lines of force of the electromagneticfield winding very closely round the electrodes and'in said fieldtherefore substantially retaining such a form as also to surround theelectrodes at the striking point. 25

If difierent types of current be employed for the working andenergislngcurrents, i. e. direct current as working current andalternating current as energising current or vice versa, the arc willnot be extinguished but will travel to and 80 fro on the electrode, theresulting are being thus evenly distributed on both sides of theelectrode. 0n the other hand if direct current, or alternating current,be exclusively employed, the arc will assume the form of a stationarysemi-cir- 35 cular disc. In such case the current energising theelectromagnetic field can be generated, in a particularly simple manneras shown in the drawing, in a transformer energised by the workingcurrent, and, if alternating current be 40 employed, the correct phaserelation between the working current and the energising current isautomatically obtained.

When heating solid or liquid substances disposed on the hearth of thefurnace, for-instance when applying the invention to a horizontal drumfurnace, and when the electrodes are arranged horizontally and eitheronly direct, or only alternating, current is used, the semicircular arcmay be directed downwards and may be caused to playdirectly on thecharge material, whilst the ceiling of the furnace is thus protected. Insuch case, when the charge to be melted is a conductor, the arc isstruck not only between the two electrodes, but also between eachelectrode and the conducting charge material, whereby a particularlyfavourable utilisation of energy is assured.

In order to avoid extinction of the arc when operating solely withalternating current, alternating currents of diiferent frequencies canbe employed for the working current and for the energising current,provided that both frequencies are in integral proportion and that they10 have a series of zero points in common.

We claim An electric arc furnace comprising two oppos-

